The B-17 Flying Fortress shaped the air war over Western Europe like no other World War II aircraft. From the outset of fighting, it provided a strategic bombing capability that the Axis could never match. Its heavy payload, defensive armament, and rugged construction allowed the Army Air Forces to bomb heavily defended targets in Western Europe, unescorted, in daylight. While the strategic bombing campaign suffered its share of missteps and the legacy of civilian casualties is still hotly debated, the efficacy of the Flying Fortress in crippling German industry and infrastructure is not in doubt. Eighth Air Force B-17s alone dropped well over 400,000 tons of bombs on Axis-held territory from August 17, 1942 to May 8, 1945. However, 4,754 Flying Fortresses were lost or written off in the course of operations, constituting 37 percent of the production run of 12,731 airframes.
Boeing built its prototype Model 299 to a 1934 Air Corps specification for a bomber with a 2,000-lb bomb load and a radius of action of more than 1,000 miles. By 1940, the B-17, as it had come to be designated, had evolved into a capable combat aircraft. The American heavy bomber doctrine that evolved through the 1930s centered on daylight precision bombing, though in operations “precision” would be a relative term, with Eighth Air Force heavy bombers dropping 50 percent of their bombs more than 1,500 feet from their targets. The solution was to fly larger formations, putting even more aircraft under the guns of capable German fighters. B-17 armament proliferated with later models mounting up to 13 .50 caliber machine guns and carrying a crew of 10. The defensive fire of B-17s took its toll on the Luftwaffe attackers, but the survival of these formations would ultimately depend on the ability of escorts to minimize the exposure to German air defense fighters.
The EMD F7 is a 1,500 horsepower (1,100 kW) Diesel-electric locomotive produced between February 1949 and December 1953 by the Electro-Motive Division of General Motors (EMD) and General Motors Diesel (GMD).
Although originally promoted by EMD as a freight-hauling unit, the F7 was also used in passenger service hauling such trains as the Santa Fe Railway's Super Chief and El Capitan.
The F7 was the fourth model in GM-EMD's successful line of F unit locomotives, and by far the best-selling cab unit of all time. In fact, more F7s were built than all other F units combined. It succeeded the F3 model in GM-EMD's F unit sequence, and was replaced in turn by the F9. Final assembly was at GM-EMD's La Grange, Illinois, plant or GMD's London, Ontario, facility.
The F7 differed from the F3 primarily in internal equipment (mostly electrical) and some external features. Its continuous tractive effort rating was 20% higher (e.g. 40,000 lb (18,000 kg) for an F7 with 65 mph (105 km/h) gearing, compared to 32,500 lb (14,700 kg) for an F3 with the same gearing.
A total of 2,393 cab-equipped lead A units and 1,463 cabless-booster or B units were built.
Many F7s remained in service for decades, as railroads found them economical to operate and maintain. However, the locomotive was not very popular with yard crews who operated them in switching service because they were difficult to mount and dismount, and it was also nearly impossible for the engineer to see hand signals from a ground crew without leaning way outside the window. As most of these engines were bought and operated before two-way radio became standard on most American railroads, this was a major point of contention. In later years, with the advent of the "road switchers" such as the EMD GP7, F units were primarily used in "through freight" and "unit train" service where there was very little or no switching to be done.